The automotive automatic transmission has traditionally had a systematic fuel economy disadvantage compared to the manual shift transmission. Advances in control solenoid technology, however, have enhanced fuel economy and shift quality of automatic transmissions.
In automatic transmission systems, a gear shift typically occurs within about 300 msec. Much of this time is devoted to filling the clutch with fluid, and therefore, approximately, 70 msec is devoted to the shift from one gear to another. Pressure of the clutch fluid fluctuates according to shifting of the transmission, which is typically controlled by a proportional solenoid. That is, during shift, the pressure of the fluid contained by the clutch fluctuates as a result of the movement of the clutch. The rate of pressure fluctuation of the clutch fluid affects the way a passenger feels the actual shift. Complicating this matter further, the feel of the actual shift may change based on type of transmission system and automobile involved. For example, the subjective feel of a shift in a performance automobile is more apparent than the feel of shift in a luxury automobile.
FIG. 6 shows a conventional control valve 100 that may be deployed in an automatic transmission system. The control valve 100 regulates the flow of fluid from a supply chamber to an exhaust chamber relative to the pressure of fluid in the control chamber. The control valve 100 has a magnetic assembly including a solenoid 102 and actuator 114, which acts on a spool valve 104. The actuator 114 and spool valve reciprocate along the same axis 106. That is, movement of the solenoid 102 creates a force on the spool valve 104, and visa versa, as the components move along the same axis 106. As shown, the spool valve 104 and solenoid 102 are mechanically coupled but may be hydraulically coupled.
Conventionally, designers have incorporated a pressure sensor 108 in the flow path 110 between a conventional control valve 100 and the control chamber 112. In order to obtain a sufficiently short response time, the flow path 110 must be relatively short, i.e., in the range of 6 to 8 inches. This arrangement advantageously allows designers to incorporate a pressure sensor 108 into conventional designs to obtain more control over the switching characteristics of the automobile.
The conventional design has disadvantages. The physical layout of the pressure sensor and the control valve is limited to a relatively close arrangement. Further, the pressure sensor requires additional electronics to process sensed pressure to produce a signal, and relay the signal to electronics implemented relative to the control valve for adjustment. While the foregoing arrangement provides a response time sufficiently short for controlling free-wheeling clutches, a need exists to further enhance the shift quality and fuel economy of the transmission and car.
The foregoing and other objects, features, aspects and advantages of the disclosure will become more apparent from the following detailed description of the claims when taken in conjunction with the accompanying drawings.